The was the first mass extinction of organisms that could be seen with the naked human eye. There was an soon before the eon of complex life began, and there may have been mass extinctions of microbes before then, but the evidence is so thin for anything before then that scientists may never know just how many mass extinctions there were. However, bacteria and archaea, those , and those communities do not have the apparent instability of complex life’s food chains, so there may have been few mass extinctions in Precambrian times. Cyanobacteria have not fundamentally changed in billions of years, which means that its mode of living has always worked well enough to ensure its survival. No animals have anything close to such a lengthy pedigree.
Some kinds of organisms found great success with their strategies and they marginalized other kinds and even drove them to extinction, to only die off themselves in a mass extinction event, and the previously marginalized life forms flourished in the post-catastrophic biome. The rise of might have never happened without the dinosaurs’ demise. Mass extinction events account for less than five percent of all species extinctions during the , but they had a profound impact on complex life’s history; the rise of mammals is only one of many radical changes. Not only would a class of animals such as mammals thrive when their dinosaur overlords were gone, but the of mammal evolution was also influenced. It took millions of years, even tens of millions of years, for ecosystems to approach their former level of abundance and diversity after a mass extinction event, and the new biomes could appear radically different from the pre-extinction biome. The geologic periods in the eon of complex life usually have mass extinctions marking their boundaries.
Mass extinctions always have critical geophysical aspects to them, and often geochemical. Continental shelves under shallow seas, which are home to most marine life, are vulnerable to sea level and oceanic current changes. Stagnant waters, or waters that have too many nutrients dumped into them, can lose their oxygen, which triggers anoxic events that kill complex life. A continental shelf exposed to the atmosphere by a falling sea level would obviously lose its marine life, and that marine life might have had nowhere else to go. Sea levels can rise or fall for different reasons. The most obvious reason has been advancing and retreating ice sheets, as water is removed from or added to the oceans, but the aggregate continental landmass has always grown (possibly sporadically), continents can rise and can fall during the journeys of their tectonic plates, and the ocean’s collective basin has fluctuated in size, as water was hydrated into rocks, and also falling when and rising again as they fragmented. Generally, when , the continental shelves lost their marine life, and , anoxic conditions often accompanied them. There is evidence that the ozone layer has been periodically damaged, which stressed all plants and animals that the Sun directly shined on. The positions of the continents, both in relation to each other and their proximity to the equator or poles, can have dramatic effects, including impacts on global climate. Global climate changes and moving continents can turn rainforests into deserts and vice versa.
The that arrived in East Asia and the islands off of Southeast Asia existed, and virtually no changes are evident in their anatomy or technology for more than 1.5 million years, only to disappear about when arrived. Like finding refuge in the islands near Southeast Asia, those at the far end of the “known” world seem to have lived like country bumpkins for well over one million years, without any outside disturbances or benefits from their cosmopolitan homeland. The foregoing is largely my speculation on the issue, which could collapse like a house of cards with the Next Great Finding, and the lack of evidence for early fires is the biggest hurdle. Like Wrangham, I will follow those investigations of early fire with great interest. I doubt that any species that ever acquired the greatest technology in Earth's history would ever lose it, as it would have quickly become indispensable.
Throughout history society has made certain transitions.
Two major events happened soon after appeared, and their sequence seems to support the Cooking Hypotheses. The first of which was the migration of from Africa ; they spread to and by 1.8 mya (perhaps 1.6 mya in the case of Java), and . It was the , and may have become the first multi-continental member of the human line, and certainly the first widespread one. Favorable climates and a lower Himalaya range and Tibetan Plateau may have encouraged that migration. Unlike Miocene apes that began to migrate from Africa 16.5 mya, there was no unbroken forest to sustain journey to East Asia. Those migrants would have to sleep on the ground for much of the journey and were not adapted for sleeping in trees, . From today’s viewpoint, it may seem that they were adventurers, but as will also become obvious with the spread of , in one individual’s lifetime, there was probably only modest movement, expanding into the next uninhabited valley or two. Such an expansion happened one valley at a time, one generation at a time, to make it across a continent in a few thousand years for those that could adapt to changing biomes. Migrating at the same latitude would not have presented great climatic issues. As those migrations happened during the ice age, they were along southern Eurasia. There is no evidence yet that ever made it to Australia, probably because of the ocean crossing required for passage.
[tags: Crime Social Class Society Violence Essays]
The Nile River's valley made the rise of Egyptian civilization possible, and it had the Old World’s most reliable food supply. Even today, half of Egypt’s population lives on the Nile’s delta. Annual floods brought silt from deforestation and erosion from the highlands to the delta, which kept the fields fertile. Unlike the Mesopotamian disaster, salination was not a major problem for Egyptians, except at and irrigated areas above the flood line. The Egyptian and Harappan civilizations were not pristine, as they were beneficiaries of Fertile Crescent innovations, and arose from hunter-gatherer societies that did not pass through the learning and evolutionary curve for domesticating their plants and animals. Those may have been the only places on Earth where civilization first appear. If not for those regions where people domesticated plants, humanity might still be living like aboriginal Australians did for nearly 50,000 years.
With various clusters of people come various beliefs in religion.
Key events in the popular story of Jesus's life, such as the virgin birth and resurrection, were already circulating in other religions of the day. There is little evidence that Muhammad existed, and if he did, he probably lived around Jerusalem, not on the Arabian Peninsula. After a career of archeological investigation in the region where the Biblical Israel was founded, one anthropologist likened the Hebrew Bible to propaganda with tiny bits of historical truth in it, as facts are needed to help people swallow fanciful stories. To modern observers not under the , tales of people living to be nearly a thousand (), or more than 40,000 years () are not taken seriously. But literalist interpretations of ancient texts abound, whether they come from religious fundamentalists or scholars such as and who tried to explain mythical events as if ancient texts depicted literal truth. Promoting is a major component of how modern populations are controlled.